首页 | 官方网站   微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   6097篇
  免费   99篇
  国内免费   11篇
工业技术   6207篇
  2023年   17篇
  2021年   88篇
  2020年   41篇
  2019年   38篇
  2018年   58篇
  2017年   57篇
  2016年   57篇
  2015年   63篇
  2014年   77篇
  2013年   185篇
  2012年   170篇
  2011年   229篇
  2010年   155篇
  2009年   181篇
  2008年   189篇
  2007年   203篇
  2006年   196篇
  2005年   176篇
  2004年   166篇
  2003年   158篇
  2002年   164篇
  2001年   153篇
  2000年   129篇
  1999年   158篇
  1998年   661篇
  1997年   412篇
  1996年   297篇
  1995年   208篇
  1994年   206篇
  1993年   166篇
  1992年   87篇
  1991年   93篇
  1990年   90篇
  1989年   77篇
  1988年   72篇
  1987年   57篇
  1986年   69篇
  1985年   82篇
  1984年   52篇
  1983年   58篇
  1982年   43篇
  1981年   52篇
  1980年   52篇
  1979年   30篇
  1978年   22篇
  1977年   54篇
  1976年   56篇
  1975年   31篇
  1974年   15篇
  1973年   23篇
排序方式: 共有6207条查询结果,搜索用时 31 毫秒
81.
In order to realize full-color electroluminescent (EL) displays, which are expected as a dominant candidate for the future multimedia flat panel display, blue EL devices with SrGa2S4:Ce have been prepared by molecular beam epitaxy (MBE). This paper proposes a novel deposition method employing Sr metal and Ga2S4 compound as the source materials. A single-phase SrGa2S4 layer is obtained in a Ga2S3/Sr flux ratio of 60 and at the growth temperature of 560°C. We have obtained the well-saturated blue with CIE color coordinates of x=0.14, y=0.14 and brighter blue EL devices made by optimizing the growth conditions in MBE. The maximum luminance of 70 cd/m2 in comparison with the 3 cd/m2 of our previous EL devices, is achieved at a driving frequency of 1 kHz  相似文献   
82.
The occurrence of 70 pharmaceutical and personal care products (PPCPs) was investigated in the Tone River. The river has the largest basin in Japan, and the water is utilized not only for farming, but also as a source of water supply. One day in both January and October 2006, surface waters in the river and its tributaries and effluents from sewage treatment plants (STPs) directly discharging into the Tone River were collected, the location of which ranged over 150 km along the river. The 70 PPCPs in the samples were concentrated by solid phase cartridge and were measured by LC-MS/MS using three analytical methods. Fifty-seven PPCPs were detected in one or more samples. Bezafibrate, caffeine, carbamazepine, clarithromycin, crotamiton and sulpiride were frequently detected. Mass flow profiles of some PPCPs (e.g., crotamiton) were comparable to cumulative inhabitants in the basin, suggesting that these PPCPs could be markers of population. Total load of each PPCP into the basin from upstream, the tributaries, and the STPs were calculated. The contribution of selected PPCPs from the tributaries with lower sewerage system coverage was dominant compared to those from upstream and the STPs, suggesting the installation of sewerage systems is necessary to reduce the load of PPCPs in the Tone River basin.  相似文献   
83.
A combined technique of the rapid freezing, freeze substitution–fixation method and the osmium–DMSO-osmium method was devised. By this combined method we clearly observed the architecture of intracellular components in three dimensions. Morphological characteristics were generally similar to those of tissue prepared by the osmium–DMSO-osmium method but different in some respects. Mucigen droplets in intestinal goblet cells, for example, appeared as separated spheres, while in specimens prepared by chemical fixation they were observed as a mass of fused droplets. In the Golgi complex, all cisternae were extremely flat, although they usually dilated on the cis side after chemical fixation. Particles on the mitochondrial tubules of liver cells were well distinguished. They were mushroom shaped, as are those observed by negative staining. The combined method, that is, the rapid freezing, osmium–DMSO-osmium method, is thought to be effective for studying the true structure of intracellular components by scanning electron microscopy.  相似文献   
84.
This paper presents an experimental study on the development of a cyclogyro-based flying robot with a new variable angle of attack mechanism. A cyclogyro is a flying machine supported in the air by power-driven rotors that rotate about a horizontal axis, like the paddle-wheels of a steamboat. Machines of this type have been designed by some companies but there has been no record of any successful flights. Our design starts with a new variable angle of attack mechanism with an eccentric (rotational) point in addition to a rotational point connecting to a motor. The main feature of the mechanism with the eccentric rotational point is the ability to change attack of angles in accordance with the wing positions (as determined by the rotational angles of the cyclogyro) without actuators. The design parameters (wing span, the number of wings, and eccentric distance) of the flying robot are determined through a series of experiments. Experimental results show that the cyclogyro-based flying robot with the new variable angle of attack mechanism is capable of generating sufficient lift force for flying.  相似文献   
85.
86.
This paper introduces the Precise Rendering Method, which generates accurately anti-aliased and highlighted images from tessellated polygons. The Precise Rendering Method first solves the aliasing problems of hidden surface removal by using the Cross Scanline Algorithm. This algorithm can exactly calculate polygon areas projected onto each pixel by using horizontal and vertical scanlines. Aliasing artifacts in shading are then prevented by the Reflection Intergration Method, which analytically integrates the intensity of reflection in the solid angle defined by surface normals at vertices of the projected area. Several synthesized images are created to show the efficiency of the Precise Rendering Method.  相似文献   
87.
Radiation tolerance of a type IIa synthetic diamond detector was examined from irradiation of mono-energetic 14 MeV neutrons. Measurements of IV (current–voltage) characteristics and energy spectrum for 5.486 MeV alpha particles were performed after neutron irradiation. In the IV characteristics measurement, enhancement of rectification was observed after neutron irradiation of up to 2.0 × 1012 n/cm2. Concurrently with the enhancement of rectification, significant decrease in signal amplitude was observed in energy spectrum measurement for alpha particles. It is considered that these changes were due to increase in the concentration of defects acting as shallow energy levels in the forbidden band. For neutron irradiation of higher than 1.6 × 1013 n/cm2, weakening of the rectification characteristics and recovery of the signal amplitude were observed. These changes imply that deep energy levels, which were also considered to be introduced by defects, were dominant and weakened the effects of the shallow energy levels. Increase in the concentration of the deep trapping levels resulted in gradual decrease of the signal amplitude and degradation in the energy resolution. The peak for the alpha particles was obtained up to 5.5 × 1013 n/cm2.  相似文献   
88.
We tested whether minimal myocardial oxygen consumption (MVO2) for a given external work would exist in the middle of a normal contractility range as previously predicted theoretically. The left ventricle of the excised cross-circulated dog heart preparation was connected to a volume servo pump. Myocardial contractility in terms of ventricular end-systolic elastance (Emax) was gradually increased from control 8.9 +/- 3.4 (mean +/- SD) to 30.0 mmHg/(ml/100 g) by epinephrine and decreased to 1.8 mmHg/(ml/100 g) by propranolol while heart rate, end-systolic pressure and stroke work were kept constant. MVO2 was determined as the product of total coronary flow and coronary arteriovenous oxygen content difference in each contractile state. We plotted MVO2 values against E(max) values in each heart. The MVO2-E(max) relation for a constant cardiac work showed that MVO2 was minimal at the low end of the covered E(max) range. We conclude that minimal MVO2 for a given cardiac work is generally obtained at the lowest working contractility in normal dog hearts. This conclusion might pose some problems in the previous theoretical prediction as to the contractility that achieves the minimal MVO2 in a given external work.  相似文献   
89.
Piperonyl butoxide, alpha-[2-(2-butoxyethoxy)ethoxy]-4,5-methylenedioxy-2-propyltol uene, is a pesticide synergist. ICR mice of both sexes were maintained on diet containing 0, 0.1, 0.3 or 0.9% of piperonyl butoxide for 20 days. At the end of the experimental period, they were necropsied. Selected organs were weighed and serum chemistries were analyzed. In male and female mice of the 0.9% group, body weight, kidney and spleen weight were depressed in comparison to those of control group. Liver weight of the 0.3 and 0.9% group of both sexes were significantly higher than those of control group. Mice of the 0.9% group of both sexes had increased serum levels of cholesterol, total protein, gamma-glutamyl transpeptidase. Histological examination of livers from mice of the 0.9% group by light microscopy showed enlarged hepatocytes, anisonucleosis and single cell necrosis. The results indicated that subacute toxicity of piperonyl butoxide in ICR mice was directed primarily at liver.  相似文献   
90.
The authors present a real-time database system capable of collecting and delivering a large amount of information accurately at a high speed and by a simple method. This system has a microprocessor unit (MPU) for each private communication line around the main memory and coordinates the independent parallel operation for a number of these MPUs with the main memory access operation, using a fixed cyclic scan method and having all the MPUs perform multi-operation. Many advantages can be expected when this method is adopted, especially for the monitoring and control of power systems. Degradation of the system can be avoided during an information rush due to accidents, and it can be easily extended when adding to or expanding the power facilities in the future. Excellent daily maintainability can be assured, and a low overall cost can be expected  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司    京ICP备09084417号-23

京公网安备 11010802026262号